How do you find a unit vector a)parallel to and b)normal to the graph of f(x)f(x) at the indicated point. f(x)= x^3, "at" (1,1)f(x)=x3,at(1,1)?

1 Answer
Oct 3, 2017

Unit vector patallel to function at (1,1)(1,1) is 3/sqrt10hati-1/sqrt10hatj310ˆi110ˆj and normal vector is 1/sqrt10hati+3/sqrt10hatj110ˆi+310ˆj

Explanation:

The slope of tangent at f(x)=x^3f(x)=x3 at (1,1)(1,1) is f'(1) and hence slope of normal is -1/(f'(1))

Now as f(x)=x^3, f'(x)=3x^2. Slope of tangent at (1,1) is 3

and slope of normal is -1/3

Therefore equation of tangent isy-1=3(x-1) or 3x-y=2

and unit vector parallel to f(x) would be (3hati-hatj)/sqrt(1^+3^2)

or 3/sqrt10hati-1/sqrt10hatj

and equation of normal is y-1=-1/3(x-1)

i.e. 3y-3=-x+1 or x+3y=4

and unit normal vector would be (hati+3hatj)/sqrt(1^+3^2)

or 1/sqrt10hati+3/sqrt10hatj, where hati and hatj are unit vectors along x-axis and y-axis respectively.